Evidence favoring hematin catalysis over autoxidation as the dominant mechanism of lipid peroxidation in animal tissues is presented. Lipid peroxidation in Erlich ascites tumor cells and isolated electron transport particles has been studied. Random destruction of the cytochromes and a loss of catalytic activity correlate with peroxidation of the electron transport particle.Mixtures of α‐, β‐, and γ‐tocopherols show no synergistic effect. Synergism with ascorbate and citrate greatly enhance the antioxidant activity of α‐tocopherol. A tocopherol‐ascorbate‐glutathione‐triphosphopyridine nucleotide couple could act synergistically to inhibit lipid peroxidation in animal tissues.